1. Field of the Invention
This invention relates to an improved catalyst system and process for the conversion of hydrocarbons, and more specifically for the catalytic reforming of gasoline-range hydrocarbons.
2. General Background
The catalytic reforming of hydrocarbon feedstocks in the gasoline range is an important commercial process, practiced in nearly every significant petroleum refinery in the world to produce aromatic intermediates for the petrochemical industry or gasoline components with high resistance to engine knock. Demand for aromatics is growing more rapidly than the supply of feedstocks for aromatics production. Moreover, the widespread removal of lead antiknock additive from gasoline and the rising demands of high-performance internal-combustion engines are increasing the required knock resistance of the gasoline component as measured by gasoline "octane" number. The catalytic reforming unit therefore must operate more efficiently at higher severity in order to meet these increasing needs for chemical aromatics and gasoline-octane. This trend creates a need for more effective reforming processes and catalysts.
Catalytic reforming generally is applied to a feedstock rich in paraffinic and naphthenic hydrocarbons and is effected through diverse reactions: dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins, isomerization of paraffins and naphthenes, dealkylation of alkylaromatics, hydrocracking of paraffins to light hydrocarbons, and formation of coke which is deposited on the catalyst. Increased aromatics and gasoline-octane needs have turned attention to the paraffin-dehydrocyclization reaction, which is less favored kinetically in conventional reforming than formation of aromatics from naphthenes. Catalyst acidity, and particularly Bronsted acidity, has been considered to be adverse to enhanced paraffin aromatization.
The effectiveness of reforming catalysts comprising a non-acidic L-zeolite and a platinum-group metal for dehydrocyclization of paraffins is well known in the art. The use of these reforming catalysts to produce aromatics from paraffinic raffinates as well as naphthas has been disclosed. Nevertheless, commercialization of this dehydrocyclization technology has been slow following an intense and lengthy development period. Catalyst selectivity, stability, and sensitivity to contaminants such as sulfur offer potential for improvement. Increased isomerization of residual paraffins and reduced dealkylation of alkylaromatics are goals within these broader objectives.
U.S. Pat. No. 4,191,638 (Unmuth et al.) discloses reforming with a catalyst combination comprising a zeolite and a conventional catalyst. Both the zeolite and the conventional catalyst comprise a platinum-group metal and a halide, and thus are acidic. Examples of zeolites are ZSM-5, CaY and TEA-mordenite.
U.S. Pat. No. 4,418,006 (Kim et al.) discloses a physical particle-form mixture of a first catalyst which is free of zeolite and comprises a noble metal and halogen and a second catalyst comprising a zeolite and non-noble metal free of noble metals. The preferred catalyst components comprise platinum on chlorided alumina and Re, Ga or W on mordenite.
U.S. Pat. No. 5,314,854 (Galperin) teaches a bed of catalyst particles comprising a multigradient noble-metal component.
German Democratic Republic patent specification 246 555, assigned to VEB Leuna-Werke "Walter Ulbricht," discloses a catalyst mixture comprising erionite or LZ-40 type, alumina, platinum, and optionally rhenium.
None of the references disclose a physical mixture of a non-acidic large-pore zeolite comprising a platinum-group component and an acidic refractory inorganic oxide having the absence of a platinum-group metal.